The object of a vibration damper in a motor vehicle is to damp vibrations excited by the uneven road surface. In this regard, there must always be a compromise between driving safety and driving comfort. A vibration damper with a stiff damping valve arrangement having a high damping force characteristic is optimal for high driving safety. If greater comfort is demanded, the damping valve arrangement should be adjusted to be as soft as possible. It is very difficult to find this compromise in a vibration damper with a conventional, non-electronic damping valve arrangement that is adjustable by an actuator.
Damping valve arrangements with a frequency-dependent damping force characteristic are known in the art. They are outfitted with an additional electronic and/or mechanical control and switch an additional damping valve arrangement on or off depending on a compression frequency and/or rebound frequency of the vibration damper.
DE 44 41 047 C1, U.S. 2006 28 36 75 A or U.S. Pat. No. 4,953,671 A may be cited by way of example.
There are also known solutions which have a control arrangement disposed at the piston rod coaxial to the damping piston comprising a control pot and a control piston which is axially displaceably arranged in the control pot. The control piston axially limits a control space which is enclosed in the control pot and which is connected to the damping valve arrangement via an inlet connection. A spring element is arranged between the control piston and the damping valve and introduces a spring force axially into the control piston on the one hand and into the damping valve on the other hand. When the control space is filled with damping medium, the control piston displaces in direction of the damping valve and, via the spring element, increases the pressing pressure of the valve disks of the damping valve, which increases the damping force.
However, all of the known damping valve arrangements are characterized by high complexity, among other reasons because they require highly precise adjustment. In particular, it is difficult in these vibration dampers to adjust the soft damping characteristic and the hard damping characteristic without additional control means.